Process and reagent for recovery of molybdenite from copper sulfide-molybdenite flotation concentrates



United States Patent 0 PROCESS AND REAGENT FOR RECOVERY OF MO- LYBDENITE FROM COPPER SULFIDE-MOLYB- DENITE FLOTATION CON CENTRATES Blair T. Burwell, Globe, Ariz., assignor to Miami Copper Company Division of Tennessee Corporation, New York, N.Y., a corporation of Delaware No Drawing. Filed Mar. 10, 1966, Ser. No. 533,222

7 Claims. (Cl. 209-467) ABSTRACT OF THE DISCLOSURE Mixed sulfide ore containing molybdenite and one or more other sulfide minerals, notably copper sulfide and/ or iron sulfide, is subjected to froth flotation in the presence of a collector reagent for the molybdenite and a depressant reagent for the other sulfide minerals. The depressant reagent is a mixture of a naphthol azoic dye, preferably Acid Red 4, Color Index No. 14710, and an aque ous solution of an alkali metal or alkaline earth metal thiophosphate, preferably sodium thiophosphate.

This invention relates to processes of differential froth flotation, involving the depression of various metallic sulfide minerals while floating various other sulfide minerals, and to chemical reagents for the purpose. It is primarily concerned with the depression of copper and iron sulfide minerals while floating molybdenite.

In Nokes U.S. Patent No. 2,811,255 granted Oct. 29, 1957, there is given a generalized background of the art of recovering, from copper sulfide flotation concentrates, the relatively small proportion of molybdenum sulfied mineral, i.e. molybdenite, that is contained therein in instances where the copper sulfide ores being treated contain small percentages of molybdenum values. There is also disclosed a process utilizing the so-called Nokes reagent of U.S. Patent No. 2,492,936 for overcoming certain difficulties encountered in the previous use of such reagent as a depressant for the copper and iron sulfide minerals associated with the molybdenite. Thus, although use of the Nokes" reagent has eliminated the need for an expensive heating step, such as roasting, boiling, or autoclaving, to be applied to the copper sulfide flotation concentrates before differential flotation for the recovery of molybdenite, it has required a preconditioning treatment involving washing, filtration, and re-pulping for most successful application.

The flotation reagent of the present invention is related to the Nokes reagent, in that it is derived from the most commonly used form thereof, i.e. from sodium thiophosphate (Example 2, Nokes et al. Patent No. 2,492,936), but it is unique, in that it is a reaction product of sodium thiophosphate and an azo dye of naphthol azoic type.

This reaction product is highly stable in contrast to the Nokes sodium thiophosphate reagent, which breaks down quite readily to yield hydrogen sulfide. Used as a depressant for copper and iron sulfides during the flotation of molybdenite, it does not require the application of expensive processing or conditioning steps, such as roasting, autoclaving, or filtering, to the flotation pulp in advance of the flotation operation, nor does it require the use of other expensive reagents for accomplishing the desired depression of copper and iron sulfides. Moreover, it operates effectively in a highly alkaline, non-corrosive circuit; in fact, usually the higher the alkalinity, the better the reagent performs. Its cost is low and it operates over a relatively broad range of concentration, so that only a minimum of control is necessary.

Of the azo dyes of naphthol azoic type used in the preparation of the reaction product, an Eosine G dye, identified "ice as Acid Red 4, Color Index No. 14710, sodium Z-(o-methoxyphenylazo}l-naphthol-4-sulfonate, is greatly preferred for the superior results it achieves. It is obtainable commercially from American Cyanamid Company under the name of Calcocid Eosine G.

Acid Red 14, Color Index No. 14720, Acid Red 5, Color Index No. 14905, Acid Orange 7, Color Index 15510, etc., are much less effective than the above-noted Acid Red 4.

It is preferred that the more stable sodium thiophosphate Nokes reagent described in copending application Ser. No. 533,234 of Burton Corbett, filed concurrently herewith, be utilized in the making of the present reagent, although the less stable sodium thiophosphate Nokes reagent of Example 2, Nokes et al. Patent No. 2,492,936, can be employed if desired.

As disclosed in the aforementioned Nokes et al. U.S. Patent No. 2,492,936, the sodium thiophosphate solution is produced by reacting at aqueous solution of sodium hydroxide (NaOH) and phosphorous pentasulphide (P 8 in the ratio of 13 parts by weight NaOH to 10 parts by weight P 8 However, as previously mentioned, instead of following the Nokes ratio, the process of this invention preferably utilizes an increased quantity of the NaOH, resulting in a more stable sodium thiophosphate solution that will not readily decompose. Although this ratio can be increased, so that a great excess of NaOH is present, the ratio presently preferred from the standpoint of economy as well as stability is 14.3 parts NaOH to 10 parts P 5 However, stability is increased correspondingly with an increase of the quantity of NaOH above the 13 parts set forth in the patent.

In preparing the reagent of this invention in the laboratory, it is convenient to dissolve 14.3 grams of sodium hydroxide in somewhat less than 200 cc. of water in any suitable container, such as a glass beaker. The heat of solution is allowed to dissipate, either by permitting the solution to stand at room temperature until cool, or, preferably, by cooling the container with cold running water. To the cooled sodium hydroxide solution are slowly added 10 grams of phosphorous pentasulphide, with constant stirring of the solution while continuously cooling the container with cold running water. Best results have been obtained when the temperature of solution is maintained below 50 C. during addiion of the phosphorous pentasulphide. The reaction is completed in about 10 minutes and volume is brought up to 200 cc. by the addition of water. Thereupon, 0.4 g. of the dye, preferably Acid Red 4, Color Index No. 14710, is stirred into the so-derived sodium thiophosphate solution. The reaction product of this mixture is the desired flotation reagent.

The specified dye is much preferred, but any of the naphthol azoic dyes will be more or less effective. The specified quantity of dye is preferred when the proportions of the other ingredients are as specified. However, the amount can be varied considerably without seriously atfecting the results.

The reagent can be made in quantities larger than 200 cc. by using the same relative proportions of water, sodium hydroxide, phosphorous pentasulphide and the dye. However, due to the greater amount of heat evolved in the larger quantities, more care is required in heat dissipation. Also, care must be taken in the preparation of the sodium thiophosphate solution to completely dissolve the sodium hydroxide, or decomposition of the sodium thiophosphate will take place rapidly with considerable evolution of hydrogen sulfide gas.

The reagent has been found to perform better under conditions of high alkalinity, although it performs satisfactorily under a variety of alkaline and acidic conditions. Best results are obtained when the pH of the flotation pulp is no less than 11.4 and preferably about 12.0.

Because lime circuits are usual for copper flotation and because lime is alkaline, regular mill water from such circuits can be advantageously utilized in the present process to give a flotation pulp of the desired alkalinity. This is an important factor in most mills where water must be conserved. It is also important from the standpoint of eliminating need for filtration and repulping of the general copper sulfide flotation concentrates or other metallic sulfide concentrates used prior to flotation for the recovery of molybdenite.

A conventional collector reagent for the molybdenite, such as kerosene, is used along with the depressant reagent of this invention in a flotation procedure that is standard except for the presence of the novel depressant reagent.

Numerous tests on final copper concentrate samples, taken at various times during normal operations at the Copper Cities mill of the Miami Copper Division of Tennessee Corporation, Miami, Ariz., and varying in molybdenite content, have been made in accordance with the following procedure:

A 600 gram dry weight sample of concentrate was pulped in a Fagergren laboratory flotation machine with enough mill circuit water to give a final pulp density of 20% solids. A 2.0 g. quantity of calcium hydroxide was added an the pulp conditioned, with air valve closed, for approximately 30 seconds; three drops of kerosene distillate and 5 ml. of the novel depressant reagent, made with Acid Red 4, Color Index No. 14710, as previously described, were then added and the pulp conditioned, with the air valve closed, for approximately 30 seconds. The air valve was then opened and the resulting froth skimmed for 5 minutes. The froth concentrates were caught, dried, weighed and assayed. The tails were filtered, dried, weighed and assayed, and from these data the percent weight of concentrate and the distribution of the molybdenite were calculated.

The results of typical tests are shown in the following table:

Test No. Product Percent Wt. Assay, percent Distribution M052 percent It will be noted from the above that conditioning time is short and that no special procedures are required.

Although sodium thiophosphate is much preferred, because of availability, low cost, and the excellent results attained from the reagent of this invention produced therefrom, other alkali metal or alkaline earth metal thiophosphates may also be employed, but generally with less satisfaction. For example, calcium thiophosphate is much less stable than is sodium thiophosphate.

Whereas the detailed description set forth above represents what is presently believed to be the best mode of carrying out the invention, it is to be understood that variations and changes may be made without departing from the generic aspects particularly pointed out and claimed herebelow.

I claim:

1. A froth flotation process, comprising subjecting an aqueous pulp containing a molybdenum sulfide mineral and one or more other sulfide minerals, such as a copper sulfide mineral and an iron sulfide mineral, to froth flotation in the presence of a collector reagent for the molybdenum sulfide mineral and a depressant reagent for the said one or more other sulfide minerals, said depressant reagent being a mixture of a naphthol azoic dye and an aqueous solution of an alkali metal or alkaline earth metal thiophosphate.

2. The froth flotation process of claim 1, wherein the depressant reagent is a mixture of a naphthol azoic dye and an aqueous sodium thiophosphate solution.

3. The froth flotation process of claim 1, wherein the thiophosphate solution is a mixture of sodium hydroxide and phosphorous pentasulfied in a weight ratio of at least about 13 parts of the sodium hydroxide to about 10 parts of the phosphorous pentasulfide.

4. The froth flotation process of claim 1, wherein the naphthol azoic dye is Acid Red 4 dye, Color Index No. 14710.

5. The froth flotation process of claim 2, wherein the naphthol azoic dye is Acid Red 4 dye, Color Index No. 14710.

6. The froth flotation process of claim 5, wherein the composition of the depressant reagent corresponds to a mixture of about 0.4 gram of the Acid Red dye and a volume of about 200 cc. of an aqueous solution containing in said 200 cc. at least about 13 grams sodium hydroxide and about 10 grams phosphorous pentasulfide.

7. The froth flotation process of claim 6, wherein 200 cc. of the said aqueous solution contains about 14.3 grams sodium hydroxide.

References Cited UNITED STATES PATENTS 2,095,967 10/1937 Brown 209-167 2,211,686 8/1940 Booth 209-166 2,492,936 12/ 1949 Nokes 209-167 2,534,197 12/1950 Grimmel 260-200 2,664,199 12/1953 Barker 209-167 3,220,551 11/ 1965 Moyer 209-167 1,878,698 9/ 1932 Heutrich 260-200 2,538,568 1/1951 Kaiser 260-200 HARRY B. THORNTON, Primary Examiner. ROBERT HALPER, Assistant Examiner. 

